Type species of Chalcomys, usually placed as a synonym of the subgenus Akodon (Cabrera, 1961; Reig, 1987). Formerly included as a subspecies of A. urichi by Cabrera (1961), but Gardner and Patton (1976), noting the pronounced difference in diploid number, listed the two as separate species; we include urichi under Necromys (see that account). Probably more than one species yet masquerades under the name of A. aerosus (see Patton and Smith, 1992; Patton et al., 1990); status of surdus as a possible junior synonym needs resolution (see Patton and Smith, 1992). Anderson (1997) recognized baliolus as a valid subspecies for Bolivian populations.